Selection Guide for HDPE Pipes for Agricultural Irrigation: Diameter and Pressure Calculation
HDPE pipes (high-density polyethylene pipes) are widely used in agricultural irrigation due to their corrosion resistance, aging resistance, good flexibility, and convenient construction. Reasonable selection of pipe diameter and pressure level can effectively improve irrigation efficiency, reduce costs, and extend service life. This article will systematically introduce the selection method of HDPE pipes in agricultural irrigation from three aspects: selection principle, diameter calculation, and pressure level determination.
Selection principle
1. Meet the irrigation flow demand
The pipe diameter must ensure sufficient flow to avoid excessive hydraulic loss due to too small a diameter, which will affect the irrigation effect.
2. Ensure water delivery pressure
According to the terrain height difference, pipe length, and terminal equipment requirements, reasonably select the pressure level to avoid pipe bursting or insufficient water pressure.
3. Take into account economy
The larger the diameter, the higher the investment. It is necessary to optimize the pipe size and reduce the construction and operation costs on the premise of meeting the use requirements.
Calculation method for HDPE pipe diameter
1. Basic formula
Common flow-velocity formula for irrigation system to calculate pipe diameter:
Q=A×VQ = A \times VQ=A×V
Where:
Q = flow (m³/s)
A = pipe cross-sectional area (m²), A = π × (D/2)²
V = flow velocity (m/s)
2. Recommended flow velocity
Pipe Diameter Range | Recommended Flow Velocity (m/s) | Remarks |
D < 100mm | 0.6 - 1.5 | Low velocity for small diameters to avoid water hammer |
100mm ≤ D ≤ 300mm | 1.0 - 2.0 | Moderate velocity for medium diameters |
D > 300mm | 1.2 - 2.5 | Higher velocity allowed for large diameters |
3. Diameter calculation example
Assuming the design flow rate is 50m³/h, convert to m³/s:
Q=503600≈0.0139 m3/sQ = \frac{50}{3600} ≈ 0.0139 \, m³/sQ=360050≈0.0139m3/s
Take the design flow rate V = 1.5 m/s, then the pipe cross-sectional area:
A=QV=0.01391.5≈0.00927 m2A = \frac{Q}{V} = \frac{0.0139}{1.5} ≈ 0.00927 \, m²A=VQ=1.50.0139≈0.00927m2
Calculate the inner diameter D:
D=2×Aπ=2×0.009273.1416≈0.1085 m≈110mmD = 2 \times \sqrt{\frac{A}{\pi}} = 2 \times \sqrt{\frac{0.00927}{3.1416}} ≈ 0.1085 \, m ≈ 110mmD=2×πA=2×3.14160.00927≈0.1085m≈110mm
Therefore, DN110 HDPE pipe is recommended.
HDPE pipe pressure level selection
1. Common nominal pressure (PN) levels
Nominal Pressure (PN) | Maximum Working Pressure (MPa) | Application Scenario |
PN6 | 0.6 MPa | Gravity flow, low-pressure water conveyance |
PN10 | 1.0 MPa | General farmland irrigation |
PN12.5 | 1.25 MPa | Undulating terrain, medium to long-distance water transport |
PN16 | 1.6 MPa | Large elevation differences or sprinkler systems |
PN20 | 2.0 MPa | High-pressure main water supply pipelines |
2. Pressure verification formula (Hagen-William formula)
Hf=10.67×L×Q1.85C1.85×D4.87H_f = 10.67 \times \frac{L \times Q^{1.85}}{C^{1.85} \times D^{4.87}}Hf=10.67×C1.85×D4.87L×Q1.85
H_f = Head loss along the way (m)
L = Pipeline length (m)
Q = Flow rate (L/s)
C = Hagen-William roughness coefficient (HDPE takes 150)
D = Pipeline inner diameter (mm)
According to the water source pressure, head and terminal equipment requirements, after verifying the head loss, select the appropriate pressure level.
Summarize the selection process
Determine the design flow (based on the irrigation area, irrigation method, etc.).
Select a reasonable flow rate (based on pipe diameter and system type).
Calculate the pipe diameter (to ensure sufficient flow and economic rationality).
Calculate the head loss based on the terrain and pipe length.
Determine the pressure level (to meet safety and operation requirements).
Comprehensively consider cost and installation convenience to optimize the selection.
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